1. Field of the Invention
This invention relates to a zoom lens of four-unit construction.
2. Related Background Art
A telephoto zoom lens of four-unit construction comprising, in succession from the object side, a focusing lens unit having positive refractive power, a variably power lens unit having negative refractive power, a correcting lens unit having positive refractive power and a relay lens unit having positive refractive power has heretofore been put into practical use.
So, in conventional telephoto zoom lenses of four-unit construction as described above, when attention is paid to the fourth lens unit as the relay lens unit, many such zoom lenses have a structure in which the exit pupil is located beyond the image plane.
Therefore, when the principal ray of a maximum angle of view passes through that lens surface in the fourth lens unit which is most adjacent to the image plane, the emergence height of the principal ray has become great, and to secure the quantity of marginal light, it has been necessary to make the effective diameter of the lens surface which is most adjacent to the image plane great.
Also, in a zoom lens of the internal focusing type based on the conventional zoom lens of four-unit construction as described above, the full length has become great to secure the movable portion of the focusing lens unit and the height at which the principal ray of a maximum angle of view passes through the lens has become small and therefore, it has been impossible to secure the quantity of marginal light sufficiently. As a result, it has been necessary to make the effective diameter of that lens in the first lens unit which is located most adjacent to the object side great.